This invention related to pilot operated pneumatic, in other words compressed air, valves. It is particularly concerned with such pneumatic valves used for producing a very short duration, high volume flow pulse. Diaphragm valves of this type are particularly suited for use in duct collecting equipment where elongate filter bags on which dust is collected on the outside surfaces must be shocked periodically by air blasts released into the bags to dislodge the dust, the dust usually falling under gravity into a collection hopper. The dust bags and collection hopper are housed as an enclosed unit and provision is generally made to direct the pneumatic pulses into the enclosure via one end of a blow tube that has several outlets branching off, each downwardly directed into one upward facing mouth of one bag. The more quickly and fully the pneumatic valve opens, the greater is the shock effect produced by the air pulse for any particular air pressure applied to its inlet. Following the high energy pulse for dislodgement of the dust, the more quickly the valve closes the less the compressed air supply source is depleted. It is usual that many such valves are installed in conjunction with one enclosure and that they are operated in sequence and it is desirable for the overall effectiveness of the filtration process that the bags are shocked reasonably frequently. For operational economy it is desirable that the quantity of compressed air used is minimised.
The valve according to the present invention will be described with particular reference to the requirements pertinent to the dust collector application. Nonetheless, the invention has other applications where fluid flows are controlled for other purposes. For example, the valve would also be very effective where pressure pulse injection into silos, hoppers and the like is required to assist material flow by breaking up arching and bridging around downwardly tapering outflow regions. Description with reference to dust collector applications is not to be taken as a limitation to the broader applicability of the invention.
Diaphragm valves used predominantly for the dust collector applications tend to be generally "large" in valve manufactures' and users terminology, typically connectable to 20 mm to 75 mm nominal pipe sizes (3/4 to 3 inches) with the principal preponderance of demand centred around the 25 to 50 mm (1 to 2 inch) sizes. Prior art valves used analogously to the proposed use of the valve of this invention have been developed over an approximately 30 year period to the state of advancement as descried in more detail later in the specification with reference to prior art valve shown in FIG. 5. The present invention concerns a further advancement of such valves that on a size for size comparison basis provide a significantly lower consumption of compressed air whilst providing at least as effective and more accurately controllable pressure pulse delivery.